Wireless transmitter and reference signal transmission method

ABSTRACT

Disclosed are a wireless transmitter and a reference signal transmission method that improve channel estimation accuracy. In a terminal (100), which transmits a reference signal using n (n is a non-negative integer 2 or greater) band blocks (which correspond to clusters here), which are disposed with spaces therebetween in a frequency direction, a reference signal controller (106) switches the reference signal formation method of a reference signal generator (107) between a first formation method and a second formation method based on the number (n) of band blocks. In addition, a threshold value setting unit (105) adjusts a switching threshold value based on the frequency spacing between band blocks. Thus, the reference signal formation method can be selected with good accuracy and, as a result, channel estimation accuracy is further improved.

TECHNICAL FIELD

The present invention relates to a radio transmission apparatus and areference signal transmission method.

BACKGROUND ART

For an uplink channel of LTE-Advanced, which is an evolved version of3rd generation partnership project long-term evolution (3GPP LTE), usingboth contiguous frequency transmission and non-contiguous frequencytransmission is under consideration (see Non-Patent Literature 1). Thatis, in communication from each radio communication terminal apparatus(hereinafter referred to as “terminal”) to a radio communication basestation apparatus (hereinafter referred to as “base station”),contiguous frequency transmission and non-contiguous frequencytransmission are switched.

Contiguous frequency transmission is a method of transmitting a datasignal and a reference signal (RS) by allocating such signals tocontiguous frequency bands. For example, as shown in FIG. 1, incontiguous frequency transmission, a data signal and a reference signalare allocated to contiguous transmission bands. In contiguous frequencytransmission, a base station allocates contiguous frequency bands toeach terminal based on the reception quality per frequency band for eachterminal, so that it is possible to obtain frequency scheduling effects.

On the other hand, non-contiguous frequency transmission is a method oftransmitting a data signal and a reference signal by allocating suchsignals to non-contiguous frequency bands, which are dispersed in a widerange of band. For example, as shown in FIG. 2, in non-contiguousfrequency transmission, it is possible to allocate a data signal and areference signal to transmission bands which are dispersed all over thefrequency band. In non-contiguous frequency transmission, compared tocontiguous frequency transmission, the flexibility of assignment of adata signal and a reference signal to frequency bands is improved, sothat it is possible to gain greater frequency scheduling effects.Further, in non-contiguous frequency transmission, it is possible todecrease the probability that all of a data signal or a reference signalof a terminal will get in a valley in fading. That is, according tonon-contiguous transmission, it is possible to obtain frequencydiversity effects and suppress deterioration of receptioncharacteristics.

Further, in LTE, as shown in FIGS. 1 and 2, a terminal transmits a datasignal and a reference signal in the same transmission band (seeNon-Patent Literature 2). Then, a base station estimates a channelestimation value of the transmission band to which a data signal of eachterminal is allocated, using a reference signal, and demodulates thedata signal using the channel estimation value.

Further, in LTE, as a reference signal to use for propagation pathestimation of an uplink channel, an orthogonal code called a cyclicshift sequence, which has high interference suppression effects, isemployed (see Non-Patent Literature 3). Because one code sequence (ZCsequence) allocated to each base station (cell) is cyclically shifted bya different amount of cyclic shift, it is possible to obtain a pluralityof cyclic shift sequences which are orthogonal to each other. An amountof shifting between cyclic shift sequences is set greater than delaytime in a multipath channel. As shown in FIG. 3, a terminal transmits acyclic shift sequence generated using a different amount of cyclic shiftper terminal or antenna. A base station obtains a correlation valuecorresponding to each cyclic shift sequence by receiving a plurality ofcyclic shift sequences that are multiplexed in a channel and performinga correlation calculation on a received signal and a base code sequence.That is, as shown in FIG. 4, the correlation value corresponding tocyclic shift sequence (CS #2) appears at the position which is shiftedby cyclic shift width Δ from the position at which the correlation valuecorresponding to cyclic shift sequence (CS #1) appears. By settingcyclic shift width Δ greater than delay time in a multipath channel, itis possible to extract a correlation value in the period (detectionwindow) in which an incoming wave of the desired wave exists.

Here, as a method of transmitting a reference signal in non-contiguousfrequency transmission, two methods are possible. First, in transmissionmethod (a) in FIG. 5, reference signals are generated from one codesequence. That is, transmission is performed by dividing one codesequence by a width corresponding to the bandwidth of each contiguousfrequency band (hereinafter referred to as “cluster”), and allocatingthe obtained subsequence to each cluster.

On the other hand, in transmission method (b) in FIG. 6, referencesignals are generated from a plurality of code sequences. That is,transmission is performed by generating a plurality of code sequencescorresponding to the bandwidth of each cluster, and allocating each codesequence to clusters.

CITATION LIST Non Patent Literature

NPL 1

-   RI-090257, Panasonic, “System performance of uplink non-contiguous    resource allocation”    NPL 2-   3GPP TS 36.212 V8.3.0, “E-UTRA Multiplexing and channel coding    (Release 8),” 2008-05    NPL 3-   3GPP TS 36.211 V8.3.0, “Physical Channels and Modulation (Release    8),” 2008-05

SUMMARY OF INVENTION Technical Problem

However, the above-described method of transmitting a reference signalin non-contiguous frequency transmission has the following problem.

In transmission method (a), compared to transmission method (b), acoding sequence (a correlation length) can be made longer. That is,transmission method (a) has an advantage of reducing interference.Specifically, in the case where a ZC sequence is used as a codesequence, when a sequence length is N, the cross-correlation valuebetween ZC sequences will be constant at 1/√N. When sequence length Ndoubles, the cross-correlation value will be 1/√2 times, making itpossible to suppress inter-cell interference power value lower by 3 dB.

However, transmission method (a) has a problem that accuracy of channelestimation deteriorates when the number of clusters is large or channelvariation in the frequency band between clusters is significant. Asshown in FIG. 7, when transmission method (a) is adopted, a base stationobtains a correlation value (that is, a delay profile) by performingcomplex division on a received reference signal that is obtained byconnecting a reference signal received as a plurality of clusters backto one code sequence, and a reference signal replica, in the frequencydomain, and by performing IDFT processing on the result of division toconvert into the time domain. At the point where reference signals areconnected, channel variation becomes non continuous, and interferenceoccurs resulting from this noncontinuity. This interference increases asthe number of clusters is greater, because the number of noncontinuouspoints increases as the number of clusters is greater. Further, when thenumber of clusters is greater, a bandwidth per cluster becomes narrowerand a correlation length becomes smaller, decreasing interferencesuppression effects and further increasing interference effects. Asdescribed above, when interference increases, the accuracy of detectinga desired wave deteriorates and separation of a plurality of cyclicshift sequences becomes difficult, drastically deteriorating theaccuracy of channel estimation as well.

On the other hand, transmission method (b) has an advantage thatdeterioration of the accuracy of channel estimation can be preventedeven when channel variation between clusters is significant. As shown inFIG. 8, when transmission method (b) is adopted, a base station obtainsa correlation value (delay profile) by performing complex division on areceived reference signal of each cluster and a reference signalreplica, in the frequency domain, and by performing IDFT processing onthe result of division to convert into the time domain. In transmissionmethod (b), because there is no noncontinuous point of channel variationas is in transmission method (a), it is possible to prevent interferencefrom occurring.

However, transmission method (b) has a problem that, because a sequencelength per cluster (a correlation length) is shorter, compared withtransmission method (a), interference suppression effects decrease andthe accuracy of channel estimation deteriorates. For example, when thenumber of clusters is 2 and the bandwidths of the two clusters areequal, the interference level in transmission method (b) increases 3 dBgreater than the interference level in transmission method (a).

It is therefore an object of the present invention to provide a radiotransmission apparatus and a reference signal transmission method forimproving the accuracy of channel estimation.

Solution to Problem

One aspect of a radio transmission apparatus according to the presentinvention employs a configuration to have a radio transmission apparatusthat transmits a reference signal using n (n is a natural number of 2 orgreater) bandwidth blocks that are positioned at intervals from eachother in a direction of frequency, the apparatus comprising: a formationsection that forms the reference signal based on one of a firstformation method, in which n subsequences are formed as the referencesignal by dividing one base code sequence into a length to match eachbandwidth block, and a second formation method, in which n codesequences are formed as the reference signal by adjusting lengths of nbase code sequences to match each bandwidth block; and a switch sectionthat switches reference signal formation methods in the formationsection between the first formation method and the second formationmethod based on a switch threshold value and the number of the bandwidthblocks n.

One aspect of a reference signal transmission method according to thepresent invention employs a configuration to have a reference signaltransmission method of transmitting a reference signal using n (n is anatural number of 2 or greater) bandwidth blocks that are positioned atintervals from each other in a direction of frequency, the methodcomprising steps of: forming the reference signal based on one of afirst formation method, in which n subsequences are formed as thereference signal by dividing one base code sequence into a length tomatch each bandwidth block, and a second formation method, in which ncode sequences are formed as the reference signal by adjusting lengthsof n base code sequences to match each bandwidth block; and switchingreference signal formation methods in a formation section between thefirst formation method and the second formation method based on a switchthreshold value and the number of the bandwidth blocks n.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a radiotransmission apparatus and a reference signal transmission method forimproving the accuracy of channel estimation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows contiguous frequency transmission;

FIG. 2 shows non-contiguous frequency transmission;

FIG. 3 shows cyclic shift sequences;

FIG. 4 shows correlation values corresponding to cyclic shift sequences;

FIG. 5 shows reference signal transmission method (a) in non-contiguousfrequency transmission;

FIG. 6 shows reference signal transmission method (b) in non-contiguousfrequency transmission;

FIG. 7 shows a problem in reference signal transmission method (a);

FIG. 8 shows a problem in reference signal transmission method (b);

FIG. 9 is a block diagram showing a configuration of a terminalaccording to Embodiment 1 of the present invention;

FIG. 10 is a block diagram showing a configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 11 is a block diagram showing a configuration of the channelestimation section in FIG. 10;

FIG. 12 shows a relationship between the first reference signalformation method and the second reference signal formation methodaccording to Embodiment 1;

FIG. 13 shows switch control between the first reference signalformation method and the second reference signal formation methodaccording to Embodiment 1;

FIG. 14 shows adjustment of threshold values used to switch referencesignal formation methods;

FIG. 15 shows switch control between the first reference signalformation method and the second reference signal formation methodaccording to Embodiment 1;

FIG. 16 shows an embodiment when applied to LTE-Advanced;

FIG. 17 shows a relationship between the first reference signalformation method and the second reference signal formation methodaccording to Embodiment 2;

FIG. 18 shows switch control between the first reference signalformation method and the second reference signal formation methodaccording to Embodiment 2; and

FIG. 19 shows adjustment of threshold values used to switch referencesignal formation methods.

DESCRIPTION OF EMBODIMENTS

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings.

Embodiment 1

[Configuration of Terminal]

FIG. 9 is a block diagram showing a configuration of terminal 100according to Embodiment 1 of the present invention. In FIG. 9, terminal100 is provided with RF reception section 101, demodulation section 102,decoding section 103, resource assignment information setting section104, threshold value setting section 105, reference signal controlsection 106, reference signal generation section 107, encoding section108, modulation section 109, fast Fourier transform (FFT) section 110,mapping section 111, inverse fast Fourier transform (IFFT) section 112,and RF transmission section 113.

RF reception section 101 performs reception processing such asdown-conversion and A/D conversion on a signal received via an antenna,and outputs the signal on which reception processing is performed todemodulation section 102.

Demodulation section 102 performs equalization processing anddemodulation processing on the signal received from RF reception section101, and outputs the processed signal to decoding section 103.

Decoding section 103 performs decoding processing on the signal receivedfrom demodulation section 102 and extracts reception data and controlinformation.

Encoding section 108 encodes transmission data and outputs the obtainedencoded data to modulation section 109.

Modulation section 109 modulates the encoded data received from encodingsection 108 and outputs the modulated signal to FFT section 110.

FFT section 110 performs FFT processing on the modulated signal receivedfrom modulation section 109 and outputs the obtained signal to mappingsection 111.

Mapping section 111 maps a data signal received from FFT section 110 anda reference signal received from reference signal generation section 107to a frequency domain resource according to a frequency assignmentinformation received from resource assignment information settingsection 104, and outputs the obtained signal to IFFT section 112.

Threshold value setting section 105 adjusts a switch threshold value inreference signal control section 106. Threshold value setting section105 receives information about clusters from resource assignmentinformation setting section 104 and adjusts a switch threshold value inreference signal control section 106 based on a frequency intervalbetween clusters.

Reference signal control section 106 receives information about clustersfrom resource assignment information setting section 104, compares whichone of the number of clusters and the switch threshold value is smalleror greater, and, based on the result of the comparison, determines amethod of forming a reference signal in reference signal generationsection 107. Reference signal control section 106 switches referencesignal formation methods in reference signal generation section 107 byoutputting identification information of the determined reference signalformation method to reference signal generation section 107.

Resource assignment information setting section 104 outputs frequencyassignment information about a reference signal and a data signal,including the number of clusters, a frequency position and a bandwidthof each cluster, to threshold value setting section 105, referencesignal control section 106, and mapping section 111. Contents ofresource assignment information are reported from base station 200(described later) to terminal 100, and are input to resource assignmentinformation setting section 104 via RF reception section 101,demodulation section 102, and decoding section 103.

Reference signal generation section 107 generates a reference signalbased on a reference signal formation method indicated by identificationinformation received from reference signal control section 106, andoutputs the reference signal to mapping section 111. As methods offorming a reference signal, as described above, there are a firstformation method (transmission method, (a)), in which subsequencescorresponding to the number of clusters are formed as a reference signalby dividing one base code sequence into the length to match eachcluster, and a second formation method (transmission method (b)), inwhich base code sequences corresponding to the number of clusters areformed as a reference signal by adjusting lengths of base code sequencescorresponding to the number of clusters to match each cluster.

IFFT section 112 performs IFFT processing on the signal received frommapping section 111 and outputs the obtained signal to RF transmissionsection 113.

RF transmission section 113 performs transmission processing such as D/Aconversion, up-conversion, and amplification on the signal received fromIFFT section 112, and trans' its the obtained signal by air to basestation 200 via an antenna.

[Configuration of Base Station]

FIG. 10 is a block diagram showing a configuration of base station 200according to Embodiment 1 of the present invention. In FIG. 10, basestation 200 is provided with RF reception section 201, discrete Fouriertransform (DFT) section 202, demapping section 203, resource assignmentinformation setting section 204, threshold value setting section 205,channel estimation control section 206, channel estimation section 207,frequency domain equalization section 208, IFFT section 209,demodulation section 210, and decoding section 211.

RF reception section 201 performs reception processing such asdown-conversion and A/D conversion on a signal received via an antenna,and outputs the obtained signal to DFT section 202.

DFT section 202 performs DFT processing on the signal received from RFreception section 201 to convert a time domain signal into a frequencydomain signal. Then, DFT section 202 outputs the frequency domain signalto demapping section 203.

Demapping section 203 extracts a data signal and a reference signal fromthe frequency domain signal received from DFT section 202 according tothe frequency assignment information received from resource assignmentinformation setting section 204. Then, demapping section 203 outputs theextracted data signal to frequency domain equalization section 208 andoutputs the reference signal to channel estimation section 207.

Resource assignment information setting section 204 outputs a frequencyassignment information that is allocated to terminal 100, including thenumber of clusters, a frequency position and a bandwidth of eachcluster, to threshold value setting section 205, channel estimationcontrol section 206, and demapping section 203. In this regard, contentsof resource assignment information are reported from base station 200 toterminal 100 in advance.

Threshold value setting section 205 adjusts a switch threshold value inchannel estimation control section 206. Threshold value setting section205 receives information about clusters from resource assignmentinformation setting section 204, and adjusts the switch threshold valuein channel estimation control section 206 based on the frequencyinterval between clusters.

Channel estimation control section 206 switches a channel estimationmethod in channel estimation section 207 to a channel estimation methodcorresponding to the reference signal transmission method in terminal100. That is, channel estimation control section 206 receivesinformation about clusters from resource assignment information settingsection 204, compares which one of the number of clusters and a switchthreshold value is smaller or greater, and, based on the result of thecomparison, determines a channel estimation method in channel estimationsection 207. Channel estimation control section 206 switches channelestimation methods in channel estimation section 207 by outputtingidentification information of the determined channel estimation methodto channel estimation section 207.

Channel estimation section 207 performs channel estimation using thechannel estimation method indicated by identification informationreceived from channel estimation control section 206, and outputs theresult of channel estimation to frequency domain equalization section208. A configuration of channel estimation section 207 will be describedin detail later.

Frequency domain equalization section 208 performs equalizationprocessing on the data signal received from demapping section 203 usingthe channel estimation result (i.e. a channel frequency response)received from channel estimation section 207. Then, frequency domainequalization section 208 outputs the result of equalization processingto IFFT section 209.

IFFT section 209 performs IFFT processing on the data signal receivedfrom frequency domain equalization section 208 and outputs the obtainedsignal to demodulation section 210.

Demodulation section 210 performs demodulation processing on the signalreceived from IFFT section 209 and outputs the obtained signal todecoding section 211.

Decoding section 211 performs decoding processing on the signal receivedfrom demodulation section 210, and outputs the obtained reception data.

FIG. 11 is a block diagram showing a configuration of channel estimationsection 207. In FIG. 11, channel estimation section 207 is provided withswitching switch 220, estimation processing section 230, and estimationprocessing section 240.

Switching switch 220 redirects the output of the reference signalreceived from demapping section 203 to estimation processing section 230or estimation processing section 240 based on identification informationreceived from channel estimation control section 206.

Estimation processing section 230 performs a first channel estimationmethod corresponding to the first reference signal formation method.Estimation processing section 230 is provided with cluster combinationsection 231, division section 232, IFFT section 233, mask processingsection 234, and DFT section 235.

Cluster combination section 231 connects, in a frequency domain, aplurality of clusters used to transmit a reference signal in terminal100, and outputs the received reference signal thus obtained to divisionsection 232.

Division section 232 performs complex division on the received referencesignal received from cluster combination section 231 using the referencesignal replica (i.e. the reference signal transmitted from terminal100). Then, division section 232 outputs the result of division (i.e. acorrelation value) to IFFT section 233.

IFFT section 233 performs IFFT processing on the signal received fromdivision section 232, and outputs the obtained signal to mask processingsection 234.

Mask processing section 234, as an extraction means of a requesteddesired wave, extracts a correlation value at a period (a detectionwindow) in which a correlation value of the desired cyclic shiftsequence by performing mask processing on the signal received from IFFTsection 233, which is equivalent to a delay profile, based on an amountof cyclic shift used in terminal 100. Then, mask processing section 234outputs the extracted correlation value to DFT section 235.

DFT section 235 performs DFT processing on the correlation value inputfrom mask processing section 234 and outputs the obtained signal tofrequency domain equalization section 208. This signal output from DFTsection 235 is a channel estimation value in which channel variation(i.e. a channel frequency response) is estimated.

Estimation processing section 240 performs a second channel estimationmethod corresponding to the second reference signal formation method.Estimation processing section 240 is provided with cluster extractionsection 241 and estimation value calculation sections 242-1 to n whichcorrespond to each cluster. Estimation value calculation section 242 isprovided with division section 243, IFFT section 244, mask processingsection 245, and DFT section 246.

Cluster extraction section 241 outputs each of the number of clusters nused to transmit a reference signal in terminal 100 to estimation valuecalculation sections 242-1 to n. Estimation value calculation section242 performs the same processing as performed in division section 232,IFFT section 233, mask processing section 234, and DFT section 235.

[Operation of Terminal]

Terminal 100 having the above configuration will be described below.

As described above, in terminal 100, reference signal control section106 switches reference signal formation methods by controlling referencesignal generation section 107.

The above-described first reference signal formation method(transmission method (a)) and second reference signal formation method(transmission method (b)) have the relationship shown in FIG. 12. Thatis, the accuracy of channel estimation is constant regardless of thenumber of clusters when the second reference signal formation method isused. On the other hand, the accuracy of channel estimation tends tolower as the number of clusters increases when the first referencesignal formation method is used. Therefore, with a certain number ofclusters N being a threshold, the accuracy of channel estimation of thefirst reference signal formation method and the accuracy of channelestimation of the second reference signal formation method are reversed.That is, when the number of clusters is N or smaller, the channelestimation value of the first reference signal formation method exceedsthe channel estimation value of the second reference signal formationmethod, while, inversely, when the number of clusters is greater than N,the channel estimation value of the second reference signal formationmethod exceeds the channel estimation value of the first referencesignal formation method.

Therefore, by using the number of clusters of a point at which theaccuracy of channel estimation of the first reference signal formationmethod and the accuracy of channel estimation of the second referencesignal formation method are reversed as a switch threshold value, it ispossible to select a more advantageous reference signal formation methodwith respect to the accuracy of channel estimation according to thenumber of clusters. By performing this kind of switch control ofreference signal formation methods, base station 200 can obtain theaccuracy of channel estimation shown with the solid line in FIG. 13.

Further, as shown in FIG. 14, the accuracy of channel estimation of thefirst reference signal formation method depends on the frequencyinterval between clusters. That is, the accuracy curve of channelestimation shifts upward as the frequency interval between clusters isnarrower. Therefore, when the frequency interval between clusterschanges, the point at which the accuracy of channel estimation of thefirst reference signal formation method and the accuracy of channelestimation of the second reference signal formation method are reversedalso shifts.

Therefore, because threshold value setting section 105 adjusts a switchthreshold value in reference signal control section 106 based on thefrequency interval between clusters, it is possible to accurately selecta reference signal formation method.

The above-described switch control of a transmission method in terminal100 is summarized in FIG. 15. That is, when the frequency interval is Yor greater, N1 is used as a switch threshold value, and transmissionmethod (a) and transmission method (b) are switched based on which oneof this threshold value and the number of clusters is smaller orgreater. On the other hand, when the frequency interval is smaller thanY, N2 is used as a switch threshold value.

As described above, according to the present embodiment, in terminal 100that transmits a reference signal using n (n is a natural number of 2 orgreater) band blocks (here, equivalent to clusters) which are positionedat intervals from each other in a direction of frequency, referencesignal control section 106 switches the reference signal formationmethods in reference signal generation section 107 between the firstformation method and the second formation method, based on the number ofband blocks n.

By this means, it is possible to select a more advantageous referencesignal formation method with respect to the accuracy of channelestimation, and, as a result of this, it is possible to improve theaccuracy of channel estimation.

Further, in terminal 100, threshold value setting section 105 adjuststhe switch threshold value based on the frequency interval between bandblocks.

By this means, it is possible to accurately select a reference signalformation method, and, as a result of this, it is possible to furtherimprove the accuracy of channel estimation.

Further, a case has been described with the above description where eachcluster is treated as a band block. However, the present invention is byno means limited to this, and it is equally possible to use a band blockformed with a plurality of clusters as an equivalent of the clusterdescribed in Embodiment 1. That is, when there are a plurality of bandblocks formed with a plurality of clusters, it is possible to employ afirst formation method in which subsequences corresponding to the numberof band blocks are formed as a reference signal by dividing one basecode sequence into the length to match each band block, and a secondformation method in which code sequences corresponding to the number ofband blocks are formed as a reference signal by adjusting the lengths ofbase code sequences corresponding to the number of band blocks to matcheach band block.

For example, a component carrier, which is a predetermined systembandwidth in LTE-Advanced, is equivalent to this band block. For acomponent carrier, a maximum value of the number of clusters that can becontained is defined by, for example, restricting the signaling format.Therefore, in such a case, it is possible to switch reference signaltransmission methods according to the number of component carriers. Forexample, in the case where the maximum value of the number of clustersin component carrier is 2, as shown in FIG. 16, it is possible to obtainthe same effects as in above Embodiment 1 even by selecting transmissionmethod (a) when the number of component carriers is 1, while selectingtransmission method (h) when the number of component carriers is 2 orgreater.

Embodiment 2

A case will be described here with Embodiment 2 where reference signalformation methods are switched based on a “cluster bandwidth.” That is,reference signal formation methods are switched based on a totalbandwidth of n clusters in addition to a switch threshold value and thenumber of clusters n. Further, basic configurations of a terminal and abase station according to the present embodiment are the same as theconfigurations of the terminal and the base station explained inEmbodiment 1. Therefore, the terminal and the base station according tothe present Embodiment will also be explained using FIGS. 9 and 10.

[Configuration of Terminal]

Reference signal control section 106 in terminal 100 according toEmbodiment 2 receives information about clusters from resourceassignment information setting section 104, and first calculates a“cluster bandwidth.” This “cluster bandwidth” means an average bandwidthper cluster and can be obtained by dividing a total bandwidth of nclusters by the number of clusters n.

Then, reference signal control section 106 compares which one of thecluster bandwidth and a switch threshold value is smaller or greater,and, based on the result of the comparison, determines a referencesignal formation method in reference signal generation section 107.Reference signal control section 106 switches reference signal formationmethods in reference signal generation section 107 by outputtingidentification information of the determined reference signal formationmethod to reference signal generation section 107.

[Configuration of Base Station]

Further, channel estimation control section 206 in base station 200according to Embodiment 2 switches the channel estimation method inchannel estimation section 207 to the channel estimation methodcorresponding to the reference signal transmission method in terminal100. That is, channel estimation control section 206 receivesinformation about clusters from resource assignment information settingsection 204, and first calculates a “cluster bandwidth,” as is the casewith reference signal control section 106.

Then, channel estimation control section 206 compares which one of thecluster bandwidth and a switch threshold value is smaller or greater,and, based on the result of the comparison, determines a referencesignal formation method in reference signal generation section 107.Channel estimation control section 206 switches channel estimationmethods in channel estimation section 207 by outputting identificationinformation of the determined channel estimation method to channelestimation section 207.

[Operation of Terminal]

As described above, in terminal 100, reference signal control section106 switches reference signal formation methods by controlling referencesignal generation section 107.

The above-described first reference signal formation method(transmission method (a)) and second reference signal formation method(transmission method (b)) have a relationship shown in FIG. 17, when thehorizontal axis of the graph shows a cluster bandwidth.

Especially, as shown in FIG. 17, the performance of transmission method(a) depends on the cluster bandwidth and deteriorates as the clusterbandwidth is narrower. When the cluster bandwidth is narrower, thenumber of clusters tends to increase. Therefore, when the number ofnon-continuous points in channel variation in calculating channelestimation increases, interference increases. Further, the performanceof transmission method (b) also depends on the cluster bandwidth anddeteriorates as the cluster bandwidth is narrower. Because thecorrelation length becomes smaller according to the cluster bandwidth,the interference suppression effects are lowered. This performancedeterioration in transmission method (b) is greater than the performancedeterioration in transmission method (a).

On the other hand, the performance in transmission method (b) is greaterthan the performance in transmission method (a) when the clusterbandwidth is wider. In transmission method (b), when the clusterbandwidth is greater, sufficient interference suppression effects can beobtained and interference can be suppressed to a noise level. Further,while, in transmission method (b), the performance does not deteriorateeven the number of clusters is large, in transmission method (a), greatinterference due to non-continuous of channel variation occurs even whenthe cluster bandwidth is wide.

That is, here again, with a certain cluster bandwidth M being athreshold, the accuracy of channel estimation of the first referencesignal formation method and the accuracy of channel estimation of thesecond reference signal formation method are reversed. That is, when thecluster bandwidth is M or narrower, the channel estimation value of thefirst reference signal formation method exceeds the channel estimationvalue of the second reference signal formation method, while, inversely,when the cluster bandwidth is wider than M, the channel estimation valueof the second reference signal formation method exceeds the channelestimation value of the first reference signal formation method.

Therefore, by using a cluster bandwidth of the point at which theaccuracy of channel estimation of the first reference signal formationmethod and the accuracy of channel estimation of the second referencesignal formation method are reversed as a switch threshold value, it ispossible to select a more advantageous reference signal formation methodwith respect to the accuracy of channel estimation according to thecluster bandwidth. By performing this kind of switch control ofreference signal formation methods, base station 200 can obtain theaccuracy of channel estimation shown with the solid line in FIG. 18.

Further, as shown in FIG. 19, the accuracy of channel estimation of thefirst reference signal formation method depends on the frequencyinterval between clusters even when the horizontal axis of the graphshows a cluster bandwidth. That is, the accuracy curve of channelestimation shifts upward as the frequency interval between clusters isnarrower. Therefore, when the frequency interval between clusterschanges, the point at which the accuracy of channel estimation of thefirst reference signal formation method and the accuracy of channelestimation of the second reference signal formation method are reversedalso shifts.

Therefore, because threshold value setting section 105 adjusts a switchthreshold value in reference signal control section 106 based on thefrequency interval between clusters, it is possible to accurately selecta reference signal formation method.

As described above, according to the present embodiment, in terminal100, reference signal control section 106 switches reference signalformation methods based on the “cluster bandwidth.” That is, referencesignal formation methods are switched based on a total bandwidth of nclusters in addition to a switch threshold value and the number ofclusters n.

By this means, it is possible select a more advantageous referencesignal formation method with respect to the accuracy of channelestimation, and, as a result of this, it is possible to improve theaccuracy of channel estimation.

Although cases have been described with the above embodiments wherereference signal formation methods are switched based on the clusterbandwidth, it is possible to use the narrowest bandwidth out of thebandwidths of n clusters instead of the cluster bandwidth.

Other Embodiment

Cases have been described with above Embodiment 1 and Embodiment 2 whereboth of reference signal transmission methods in terminal 100 andchannel estimation methods in base station 200 switch according to thenumber of clusters or a cluster bandwidth. However, it is possible toswitch only channel estimation methods in base station 200. That is, itis possible to fix the reference signal transmission method in terminal100 to transmission method (a) or transmission method (b), and switchchannel estimation methods in base station 200 according to the numberof clusters or a cluster bandwidth. By this means, it is also possibleto obtain effects similar to the effects of Embodiment 1 and Embodiment2.

Also, although cases have been described with the above embodiments asexamples where the present invention is configured by hardware, thepresent invention can also be realized by software.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of a programmableFPGA (Field. Programmable Gate Array) or a reconfigurable processorwhere connections and settings of circuit cells within an LSI can bereconfigured is also possible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2009-018632, filed onJan. 29, 2009, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

A radio transmission apparatus and a reference signal transmissionmethod according to the present invention are useful for improving theaccuracy of channel estimation.

The invention claimed is:
 1. A transmission apparatus comprising: areceiver, which, in operation, receives, from a base station, allocationinformation indicating one or two sets of consecutive frequencyresources allocated in each of one or more uplink component carriers,which include a first component carrier and a second component carrierwhen more than one uplink component carrier are configured, the firstcomponent carrier and the second component carrier having differentfrequency, and the two sets of consecutive frequency resources beingspaced apart from each other along a frequency axis; circuitry, which,in operation, based on the received allocation information, performs oneof: a first operation of generating plural uplink reference signalsequences including a first sequence and a second sequence, mapping thegenerated first sequence in said one or two sets of consecutivefrequency resources allocated in the first component carrier, mappingthe generated second sequence in said one or two sets of consecutivefrequency resources allocated in the second component carrier, andcontrolling transmission of the mapped first sequence and the mappedsecond sequence; and a second operation of generating one uplinkreference signal sequence, mapping the generated one uplink referencesignal sequence in said two sets of consecutive frequency resourcesallocated in said one uplink component carrier by dividing the generatedone uplink reference signal sequence into two subsequencescorrespondingly to said two sets of consecutive frequency resources,respectively, and controlling transmission of the mapped one uplinkreference signal sequence, wherein the first operation and the secondoperation are switched based on a number of said one or more uplinkcomponent carriers.
 2. The transmission apparatus according to claim 1,wherein the generated one or plural uplink reference signal sequence(s)are cyclic shift sequences.
 3. The transmission apparatus according toclaim 1, wherein when a number of said one or more uplink componentcarriers is two, a number of the generated plural uplink referencesignal sequences is two.
 4. The transmission apparatus according toclaim 1, wherein a sequence number of the generated first sequence isdifferent from a sequence number of the generated second sequence. 5.The transmission apparatus according to claim 1, wherein a first lengthof the generated first sequence corresponds to a bandwidth of the one ortwo sets of consecutive frequency resources allocated in the firstcomponent carrier, and a second length of the generated second sequencecorresponds to a bandwidth of the one or two sets of consecutivefrequency resources allocated in the second component carrier.
 6. Thetransmission apparatus according to claim 1, wherein a length of thegenerated first sequence mapped in one set of consecutive frequencyresources allocated in the first component carrier is different from alength of the generated second sequence mapped in two sets ofconsecutive frequency resources allocated in the second componentcarrier.
 7. A transmission method performed by a transmission apparatus,the transmission method comprising: receiving, from a base station,allocation information indicating one or two sets of consecutivefrequency resources allocated in each of one or more uplink componentcarriers, which include a first component carrier and a second componentcarrier when more than one uplink component carrier are configured, thefirst component carrier and the second component carrier havingdifferent frequency, and the two sets of consecutive frequency resourcesbeing spaced apart from each other along a frequency axis; performing,based on the received allocation information, one of: a first operationof generating plural uplink reference signal sequences including a firstsequence and a second sequence, mapping the generated first sequence insaid one or two sets of consecutive frequency resources allocated in thefirst component carrier, mapping the generated second sequence in saidone or two sets of consecutive frequency resources allocated in thesecond component carrier, and transmitting the mapped first sequence andthe mapped second sequence; and a second operation of generating oneuplink reference signal sequence, mapping the generated one uplinkreference signal sequence in said two sets of consecutive frequencyresources allocated in said one uplink component carrier by dividing thegenerated one uplink reference signal sequence into two subsequencescorrespondingly to said two sets of consecutive frequency resources,respectively, and transmitting the mapped one uplink reference signalsequence, wherein the first operation and the second operation areswitched based on a number of said one or more uplink componentcarriers.
 8. The transmission method according to claim 7, wherein thegenerated one or plural uplink reference(s) signal sequences are cyclicshift sequences.
 9. The transmission method according to claim 7,wherein when a number of said one or more uplink component carriers istwo, a number of the generated plural uplink reference signal sequencesis two.
 10. The transmission method according to claim 7, wherein asequence number of the generated first sequence is different from asequence number of the generated second sequence.
 11. The transmissionmethod according to claim 7, wherein a first length of the generatedfirst sequence corresponds to a bandwidth of the one or two sets ofconsecutive frequency resources allocated in the first componentcarrier, and a second length of the generated second sequencecorresponds to a bandwidth of the one or two sets of consecutivefrequency resources allocated in the second component carrier.
 12. Thetransmission method according to claim 7, wherein a length of thegenerated first sequence mapped in one set of consecutive frequencyresources allocated in the first component carrier is different from alength of the generated second sequence mapped in two sets ofconsecutive frequency resources allocated in the second componentcarrier.